path: root/arch/x86/mm/pat.c

/*
 * Handle caching attributes in page tables (PAT)
 *
 * Authors: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
 *          Suresh B Siddha <suresh.b.siddha@intel.com>
 *
 * Loosely based on earlier PAT patchset from Eric Biederman and Andi Kleen.
 */

#include <linux/seq_file.h>
#include <linux/bootmem.h>
#include <linux/debugfs.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/rbtree.h>

#include <asm/cacheflush.h>
#include <asm/processor.h>
#include <asm/tlbflush.h>
#include <asm/x86_init.h>
#include <asm/pgtable.h>
#include <asm/fcntl.h>
#include <asm/e820.h>
#include <asm/mtrr.h>
#include <asm/page.h>
#include <asm/msr.h>
#include <asm/pat.h>
#include <asm/io.h>

#ifdef CONFIG_X86_PAT
int __read_mostly pat_enabled = 1;

static inline void pat_disable(const char *reason)
{
	pat_enabled = 0;
	printk(KERN_INFO "%s\n", reason);
}

static int __init nopat(char *str)
{
	pat_disable("PAT support disabled.");
	return 0;
}
early_param("nopat", nopat);
#else
static inline void pat_disable(const char *reason)
{
	(void)reason;
}
#endif


static int debug_enable;

static int __init pat_debug_setup(char *str)
{
	debug_enable = 1;
	return 0;
}
__setup("debugpat", pat_debug_setup);

#define dprintk(fmt, arg...) \
	do { if (debug_enable) printk(KERN_INFO fmt, ##arg); } while (0)


static u64 __read_mostly boot_pat_state;

enum {
	PAT_UC = 0,		/* uncached */
	PAT_WC = 1,		/* Write combining */
	PAT_WT = 4,		/* Write Through */
	PAT_WP = 5,		/* Write Protected */
	PAT_WB = 6,		/* Write Back (default) */
	PAT_UC_MINUS = 7,	/* UC, but can be overriden by MTRR */
};

#define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))

void pat_init(void)
{
	u64 pat;
	bool boot_cpu = !boot_pat_state;

	if (!pat_enabled)
		return;

	if (!cpu_has_pat) {
		if (!boot_pat_state) {
			pat_disable("PAT not supported by CPU.");
			return;
		} else {
			/*
			 * If this happens we are on a secondary CPU, but
			 * switched to PAT on the boot CPU. We have no way to
			 * undo PAT.
			 */
			printk(KERN_ERR "PAT enabled, "
			       "but not supported by secondary CPU\n");
			BUG();
		}
	}

	/* Set PWT to Write-Combining. All other bits stay the same */
	/*
	 * PTE encoding used in Linux:
	 *      PAT
	 *      |PCD
	 *      ||PWT
	 *      |||
	 *      000 WB		_PAGE_CACHE_WB
	 *      001 WC		_PAGE_CACHE_WC
	 *      010 UC-		_PAGE_CACHE_UC_MINUS
	 *      011 UC		_PAGE_CACHE_UC
	 * PAT bit unused
	 */
	pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) |
	      PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);

	/* Boot CPU check */
	if (!boot_pat_state)
		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);

	wrmsrl(MSR_IA32_CR_PAT, pat);

	if (boot_cpu)
		printk(KERN_INFO "x86 PAT enabled: cpu %d, old 0x%Lx, new 0x%Lx\n",
		       smp_processor_id(), boot_pat_state, pat);
}

#undef PAT

static char *cattr_name(unsigned long flags)
{
	switch (flags & _PAGE_CACHE_MASK) {
	case _PAGE_CACHE_UC:		return "uncached";
	case _PAGE_CACHE_UC_MINUS:	return "uncached-minus";
	case _PAGE_CACHE_WB:		return "write-back";
	case _PAGE_CACHE_WC:		return "write-combining";
	default:			return "broken";
	}
}

/*
 * The global memtype list keeps track of memory type for specific
 * physical memory areas. Conflicting memory types in different
 * mappings can cause CPU cache corruption. To avoid this we keep track.
 *
 * The list is sorted based on starting address and can contain multiple
 * entries for each address (this allows reference counting for overlapping
 * areas). All the aliases have the same cache attributes of course.
 * Zero attributes are represented as holes.
 *
 * The data structure is a list that is also organized as an rbtree
 * sorted on the start address of memtype range.
 *
 * memtype_lock protects both the linear list and rbtree.
 */

struct memtype {
	u64			start;
	u64			end;
	unsigned long		type;
	struct list_head	nd;
	struct rb_node		rb;
};

static struct rb_root memtype_rbroot = RB_ROOT;
static LIST_HEAD(memtype_list);
static DEFINE_SPINLOCK(memtype_lock);	/* protects memtype list */

static struct memtype *memtype_rb_search(struct rb_root *root, u64 start)
{
	struct rb_node *node = root->rb_node;
	struct memtype *last_lower = NULL;

	while (node) {
		struct memtype *data = container_of(node, struct memtype,